A trial of administering oxytocin to children with autism has reported positive effects for some recipients, and provided insight into which children are most likely to benefit. In the process, the researchers got a surprising hint at the workings of the placebo effect, which despite its importance to science is very poorly understood.

In recent years there has been much excitement about the idea of giving children with autism oxytocin – known as the "love" or "trust" hormone due to the way it affects our behavior – to address negative aspects of the condition. Nevertheless, studies so far have been small, and while sometimes encouraging, have also been frequently inconsistent. The variation in benefits emphasizes the diversity lumped under the autism diagnosis.

Dr Karen Parker of Stanford University continued this work, but measured baseline oxytocin levels in the participating children first. Parker gave 14 children with autism oxytocin sprays twice daily for four weeks, while another 18 received a placebo. Most of the children also had intellectual impairments. Parker observed an average ten point improvement on the widely used Social Responsiveness Scale among the children given the active drug, and three points for those on the placebo.

Children whose pre-trial oxytocin levels were lower experienced a bigger benefit."Our results suggest ... blood oxytocin levels might be a biological sign that will allow us to predict if a child will respond maximally or not," Parker said in a statement.

Parker previously showed that even though autistic children are more likely to have low oxytocin levels, there is wide variation in these levels, both among autistic and non-autistic children. Moreover, non-autistic children with low oxytocin levels are also more likely to show social impairment. Consequently, it appears possible that the test of whether a child will benefit from oxytocin treatment is not whether they have autism or not, but what their natural levels of the hormone are.

She found that, of those on the placebo, it was the ones with the low blood oxytocin levels at the start who benefited most. Moreover, these children started producing more of their own oxytocin, which Parker said raises the possibility that the placebo effect, even for very different conditions, may be mediated by increased oxytocin production.

Several institutions are currently conducting a similar, but much larger, study, and Parker's work could provide suggestion on what to look out for. Senior author Professor Antonio Hardan, who has a clinical practice for children with autism, said that he would not advocate giving children oxytocin based on this study alone, but might if the larger project confirmed its findings.